The present invention relates to a robot arm.
The arm of a conventional humanoid robot is typically attached to the body via a shoulder joint so as to be rotatable both in the fore-and-aft and lateral directions. According to this structure, the two hands can be brought together in front of the chest only by swinging the arms forward and then laterally toward each other. Therefore, the elbows must be kept fully stretched at such a time.
However, when the humanoid robot walks in an upright position (bipedal motion) carrying a relatively heavy object, it is desirable to hold the object as close to the center of the body as possible to minimize the shift in the gravitational center of the robot. However, according to the conventional structure, because the two hands cannot be brought together immediately in front of the chest, the kinds of work which the robot is capable of were limited.
In view of such problems of the prior art, a primary object of the present invention is to provide an improved robot arm which allows the two hands to be brought together in front of the chest.
A second object of the present invention is to provide a robot arm which is capable of holding a relatively heavy object without excessively tipping the balance of the robot.
A third object of the present invention is to provide a robot arm which has an increased freedom of motion.
To achieve such an object, the present invention provides a robot arm attached to a side of a robot body, comprising: an upper arm having a base end attached a side of a robot body via a shoulder joint so as to be rotatable around a laterally extending first axial line and a second axial line perpendicular to said first axial line; a forearm having a base end attached to a free end of said upper arm via an elbow joint having bifurcated ends, said forearm base end being interposed between said bifurcated ends so as to be rotatable around a third axial line extending along the length of the upper arm and a fourth axial line perpendicular to said third axial line; and a hand attached to a free end of said forearm.
Thus, the elbow joint can be twisted with respect to the upper arm so that the hands can be brought together in front of the chest. Therefore, the robot is capable of holding a heavy object close to its chest or belly without unduly shifting the gravitational center of the robot. The freedom of motion of the arm is also enhanced.
Furthermore, if the hand is attached to the forearm so as to be rotatable around a longitudinal axial line of the forearm, the freedom of the motion of the arm can be increased even further.